1. Field of the Invention
The invention relates to the field of photographic film and improving the surface characteristics thereof.
2. Description of the Prior Art
In the use of photographic films, problems frequently arise due to surface adhesion or friction. Especially, motion picture films and narrow films must possess good slip properties to assure satisfactory running in the camera and in projectors. To achieve this, special slip agents are used which, usually applied to the back side of the film, provide improved slip properties (i.e., reduce surface friction) of the material. Known lubricants, which have been proposed so far for this purpose, mostly belong to the group of waxes or wax-like compounds as well as silicon compounds. A summarizing discussion of these materials and their use as slip agents is found in J. Soc. Motion Picture Television Engn., 74 (1965) 297-307, especially on p. 304 ff.
Recently the problem of adhesion and friction has arisen also in the case of X-ray films. For modern diagnostic functioning and for angiography, so-called sheet film exchangers are used, with which X-ray films are moved in rapid sequence in the beam path of the X-ray tube and exposed and again taken out of the beam path. The picture sequences amount to up to 10 photographs per second. Here, the problem of adhesion and friction of the films against one another as well as on the magazine walls, etc., is of great importance. Similar problems arise also in films for taking photographs in video amplifying cameras as well as in ribbon-shaped material for cineradiography.
However, if one wishes to solve this problem with slip agents which were developed predominantly for coating on the emulsion-free back side of motion picture films, it is found that they are not suitable for X-ray films. Namely, they must be introduced in the X-ray emulsion on both sides or applied on top of it, which leads to additional difficulties. Thus, silicon compounds, for example, the dimethylpolysiloxane according to German Offenlegungsschrift No. 1,938,959 cause appreciable wetting disturbances in casting, when they are added to the protective films on the X-ray emulsions. These wetting disturbances are manifested also in the processing of the films through nonuniform and delayed development and fixing. Besides, this slip agent addition leads to marked turbidity of the developed films, which cannot be tolerated in X-ray materials. Compounds of the wax type, for example, cetyl palmitate according to the German Pat. No. 1,300,015, improve the friction value sufficiently only at higher concentrations and then also display marked turbidity. The fixing speed is also reduced. Besides, it is a particular disadvantage that both types of slip agents influence unfavorably the hardening of the photographic films, which prevents the processing of the X-ray films at elevated temperatures in modern roll developing machines.
Accordingly, the problem of the invention is to develop suitable slip agents, preferably for X-ray materials.